Reliability of Led drivers is the Key to Success

1. LEDTECHNOLOGY
60 LIGHTING INDIA July-August 2018
Reliability of LED Drivers
The Key to SuccessA reliable LED driver must be equipped with thermal foldback capability;
this feature enhances the thermal management and will increase operating
life of the LED driver incredibly.
L
ED lighting with its extraordinary
visual performance (users’
viewing experience) and eye-
catching energy savings is an excellent
lighting option when compared to
traditional lighting options.
Today, LEDs have become even
more efficient than earlier generations,
providing 25-30 per cent energy savings
compared to CFLs and up to 80 per
cent savings compared to incandescent
bulbs. Along with energy savings, the
other reason driving the switch to LED-
based lighting is the significantly longer
lifespan of the LEDs.
Worldwide, LED lighting market is
growing at accelerated pace. These
efficient LEDs need compatible LED
drivers. The market expects highly
reliable, energy efficient, protective and
differentiated LED driver products at
competitive prices.
Keeping these tough design
PictureCourtesy:www.thedreamcreators.co.in
challenges in mind, Power Nucleus has
worked with Infineon to effectively meet
and exceed the market expectations
from LED drivers.
In the beginning, the lighting industry
had promised consumers a new,
affordable light source (LED) with low
energy consumption and a long life.
Unfortunately, the industry’s focus on
cutting cost to the extent of sacrificing
quality meant that the market was soon
flooded with poor quality and low-cost
products. To fulfil the initial promise to
consumers, a design revolution for a
high-quality product at low costs needs
to be the top priority for the LED lighting
industry.
The strongest need for efficient and
reliable LED drivers comes from
customers serving the street lighting
segment, where the cost of lamp
replacement is sometimes higher than
the cost of LED drivers itself. They also
need to provide 5 to 7 years of warranty
on their products. These factors are
considered during the design stage and
selection of components and topology.
ICL5101 from Infineon is a resonant
controller which offers great features to
develop efficient LED drivers. Few of its
key features include:
Universal input from 80 to 305V
Ultra-fast time to light <200ms
Secondary side-controlled PFC+LLC
or PFC+LCC (CV/CC)
Fully integrated 650V HB driver
stage
Supported outdoor use by extended
temperature range (-) 40 to (+)
125-egree C
Figure 1: Constant current performance of 150W LED Driver
This image is for representation purpose only

2. July-August 2018 LIGHTING INDIA 61
LEDTECHNOLOGY
High power quality with PFC >0.99
/ THD <10 per cent
Highest efficiency up to 94 per cent
in resonant topology
Protection: OCP / OVP / OLP / short
output
Saturation control during start-up
Adjustable ext. temperature
protection.
Constant current or constant
voltage or both
LEDs are driven with DC voltage or
current. Almost all LED drivers are
simple AC-DC power supplies. That
being the case, why is it important to
term a power supply as LED driver?
Let’s understand a little bit of background
of the LEDs.
You can drive the LEDs with constant
voltage (CV). There are many CV drivers
available in the market, but without
some kind of output current limit. With
CV drivers, the problem lies with LEDs
heating up, whereby the forward voltage
drops and the current passing through
the LED increases. Higher current leads
to more heat generated from the LED.
Without the forward current limit, the
LED will fail due to the high heat at its
junction. This type of failure is known as
thermal runaway.
The LED light output is proportional
to the forward current flowing through
it. This means, any variation in the LED
current will vary the light output as well.
This is why driving the LEDs in CV mode
results in LED lifetime issues. The
learning from this is that the LEDs
should be driven with constant current
(CC) which guarantees a constant light
output from the LEDs. Accurate and
ripple-free constant LED current is
recommended to produce excellent,
flicker-free light output.
Let’s assume that the LED load is
disconnected for some reason, or in
case of installation, wherein the input
power to the LED driver is on and no
LED current flows; since the driver is
configured in the constant current
mode, it will drive up the output voltage,
high enough to damage the output
circuits including output capacitors.
This is known as open load condition,
when driver output voltage must be
limited to a safe value when the LED
current is lower or when there is no
load. This requires the driver to operate
at constant voltage.
Drive towards high efficiency
(efficacy matters)
Many system integrators, LED
lighting contractors and even the
governments have started to demand
for more lumens per watt (>120 lm/W).
More lumens per watt means more
energy savings.
There are several ways to achieve
this. For example, one can use very high
efficiency LEDs at a higher cost. The
Figure 2: System efficiency of 150W LED driver
Figure 3: Input power factor w.r.t. input voltage of 150W LED driver
Figure 4: Input current THD performance of 150W LED driver

3. LEDTECHNOLOGY
62 LIGHTING INDIA July-August 2018
Harsh Savant
Staff Engineer for Power
Management and
Multimarket (PMM)
Division,
Infineon Technologies
India)
better way is to build highly efficient LED
driver, so that:
It meets one’s efficacy demands
easily.
Relaxes thermal management
requirements which helps to meet
more serviceable life from the driver.
Now, let’s take a look as to what it
takes to develop high efficiency LED
drivers:
Right power conversion topology
selection for the given power rating
of the LED driver.
Knowledge about the selection of
power semiconductors incl.
MOSFETs, input-output diodes with
optimum derating, without impacting
the cost of the product.
Deep knowledge about the magnetic
components design for various
power topologies (LLC converter,
PFC converter, Flyback converters,
interleaved converters). Many a
times, this is the real cause of overall
poor efficiency of the LED driver. A
power designer expert will be able to
handle with great care and do a
wonderful job.
Control the converter in such a way
that it operates at minimum losses.
The best way of doing it is to have
zero voltage switching (LLC) or quasi
resonant operation which helps to
maximise the product life and at a
lower cost.
Also, the selection of aluminium
electrolytic capacitors. These must
be rated for high load life (>8,000
hours) at maximum operating
temperature.
Advantages of selecting LLC
topology
Zero voltage switching (soft
switching) helps to lower switching
losses and improve system efficiency.
Due to lower switching losses, the
design can operate at higher
frequency which can result into
smaller magnetic components and
reduction in board size i.e., increase
in power density.
Soft switching over wide load range
– high efficiency at lower loads.
Soft switching enables less EMI –
Lower EMI component cost.
Half bridge switching enables usage
of 600V MOSFETs, unlike 800V
MOSFETs in Flyback topology.
Lower VRRM (reverse voltage) of
output diode due to lower stress in
soft switching topologies.
High efficiency in LED drivers is
achieved by using Infineon’s power
semiconductors and combo - LLC
Controller IC ICL5101.
Thermal management
While high power LEDs are running,
the lighting fixture temperature can be
quite high under some conditions. As
the drivers are generally enclosed within
the fixtures, the LED driver’s electronics
is most likely to be exposed to the same
temperature. If the LED drivers continue
to operate at such high temperatures,
their serviceable lifetimes will be
degraded significantly. The high-quality
drivers enable intelligent adaptive
temperature protection. The output
current of the LED driver starts to drop
when the thermal limit is exceeded until
the thermal is within operating range
again and the driver delivers the full
current.
To achieve this excellent requirement,
the thermal foldback feature is
implemented in all LED drivers designed
by Power Nucleus LED Drivers.
Figure 5: Thermal foldback performance of 150W LED driver
Picture & specification of 150W LED driver
• Input voltage range 90-305Vac
• Vout < 85- 110V@1.44A and configurable
• Efficiency > 93%
• PFC > 0.97, THD <6%
• EMI pre-compliance
• Protection:
– OCP – Over load
– OVP – Over voltage
– OLP – Open loop
– OTP – Over temp
• 5KV Surge
• IPA60R280P6 Mosfet used on PFC and LLC
• Output ripple < 10%
Dinesh Kumar
CEO
Power Nucleus India
Pvt. Ltd.